Arm Restraints and Safety Cams: A Car Lift Checklist

A farm shop owner southwest of the Des Moines metro asked us to look at a car lift automotive setup he found on a farm auction listing — a used 7,000 lb two-post that had spent its life in a rural machine shed. He restores old pickups and does his own metal work, so he needed something he could trust with a stripped cab shell one week and a loaded one-ton the next. We went with him to look at it. The columns were straight and the cylinders held pressure, but the arm restraint gears were worn round on three of four arms and one safety cam had been welded. He passed on it. Here is the checklist we ran that day, and why arm restraints and cam engagement top the list.

Why Arm Restraints Matter More on Restoration Work

Arm restraints exist to keep a swing arm from rotating out from under a vehicle while it is in the air. On a modern service bay with balanced, fully assembled vehicles, they are a backup system that rarely gets tested. On restoration and metal work, they get tested constantly. A stripped cab with no drivetrain, no glass, and no bed sits nowhere near its factory center of gravity. Every time you cut a rocker out or pull a fender, the load shifts. That is exactly when an unrestrained arm decides to swing.

The restraint mechanism on most two-post equipment is a spring-loaded gear that meshes with a toothed segment on the arm pivot. When the arm carriage rises off the floor, the gear drops into engagement and the arm can no longer swing. Simple, and it works — until the teeth round off from years of operators forcing arms while loaded, or until the spring rusts and stops pushing the gear down. In a rural machine shed with no heat and seasonal humidity swings, those springs corrode fast. We pull them apart, wire-wheel the gear, replace the spring, and grease the pivot. Parts are inexpensive. Skipping the check is not. If you are evaluating any used car lift automotive purchase, put your hand on each arm at full extension with the carriage raised and try to swing it. It should not move at all.

Safety-Cam Engagement: Listen, Then Look

The safety locks are the mechanical latches that hold each carriage at a fixed height so the hydraulics are not the only thing between the vehicle and the floor. On most two-post designs, spring-loaded cams drop into ladder slots inside each column as the carriage rises. Raising past a lock and then lowering onto it is the standard procedure — you lift a few inches above your working height, then release and settle onto the nearest set of locks.

You should hear both cams click at the same time on the way up. If one side clicks and the other is silent or late, something is wrong: a stretched or broken latch spring, a bent cam, debris in the ladder slot, or a cable-driven release that is out of adjustment. On the auction lift near the Des Moines metro, one cam had been welded solid because it kept dragging — which meant the operator had eliminated the ability to release that side and probably had been relying on hydraulics alone. That is not a repair, it is a hazard. We also check that the release mechanism, whether air-actuated or cable-pulled, drops both cams simultaneously. Uneven release is how carriages get out of sync and how vehicles get dropped a few inches all at once. Test this empty, at three different heights, before you put a vehicle on any car lift automotive equipment you did not install yourself.

Capacity, Weight Distribution, and Farm Shop Reality

Rated capacity is the total the lift will hold, but it also assumes a front-to-rear distribution — commonly a 50/50 or a specified maximum on one pair of arms. Restoration work breaks those assumptions. Pull the engine and transmission from a 1970s pickup and suddenly almost all the remaining weight is behind the cab. Load a bare frame with a new crossmember and a welder cart on the runway and the numbers move again.

For a farm shop doing mixed work, we generally point people at 10,000 lb rather than 7,000 lb, even when the vehicles seem light. The extra capacity buys you margin for the one-ton service truck that shows up, for the dually, and for the tractor loader bucket somebody wants to set on a stand. We also talk about arm reach. Restoration frequently means lifting vehicles with unusual frame geometry — old body-on-frame trucks with wide rails, small imports with short wheelbases, and shells with the pinch welds cut away. Asymmetric configurations with three-stage front arms handle short wheelbases well; symmetric setups with long arms front and rear suit long-bed trucks better. If you do both, a symmetric arrangement with adapter blocks and a set of tall pads is usually the more flexible choice. We keep pad and adapter kits in stock because half the calls we get about lifting problems on a car lift automotive setup turn out to be a pad height issue, not a lift issue.

Cables, Sheaves, and the Parts That Fail Quietly

Equalization cables keep both carriages traveling together. They run over sheaves at the top and bottom of each column and they wear from the inside out, which is why a cable can look fine and still be near failure. Inspect where the cable passes over each sheave — that is where the strands break first. Any broken wire, any flat spot, any kink, and the cable set gets replaced in pairs. Never one side only.

Sheaves themselves wear grooves and seize. A frozen sheave saws the cable instead of rolling with it, and it will chew a new set in months. Spin every sheave by hand during inspection. On older equipment we frequently replace bushings or the whole sheave assembly along with the cables, and we always check the anchor bolt torque while we are in there. Hydraulic components fail more visibly: seeps at cylinder rod seals, a power unit that whines and does not build pressure, hose fittings weeping at the crimp. Those are all repairable, and on a good frame they are worth repairing. What is not worth repairing is a bent column, a cracked baseplate weld, or an arm pivot that has been welded and reworked more than once. If you are unsure which category your equipment falls into, our team has evaluated hundreds of used units across Iowa — see our notes on when lift cables need replacing before you spend money.

Concrete, Anchors, and the Machine Shed Problem

Rural shop slabs are the wild card. Many farm buildings were poured in phases, some over gravel fill with no vapor barrier, and thickness can vary by several inches within one bay. A two-post lift transmits enormous tension into the anchors when a load shifts, and a four-inch slab over soft fill will let the whole baseplate tilt even if the anchors hold.

Before we set anything, we verify slab thickness with a core sample or an existing penetration, check distance to control joints and the building edge, and look for signs of settling in the surrounding floor. Minimum for most 10,000 lb units is four inches of 3,000 PSI concrete, and we prefer six. If the slab is short, the answer is a saw-cut footing pad per baseplate — roughly a three-foot square, a foot deep, tied in with dowels, cured a week. It is not glamorous work and it adds cost, but it is the difference between equipment you trust and equipment you watch nervously. We also see farm shops with in-floor heat tubing, so we ask about it every time. Anchor torque gets checked at install and again after the first thirty days of use, then annually. That single habit prevents more problems than any other maintenance item on a car lift automotive installation.

The Pre-Purchase Checklist, Condensed

Run this in order and it takes about thirty minutes. One: identify make, model, and serial number, and confirm parts are still available. Two: check all four arm restraints for engagement with the carriage raised — no swing allowed. Three: cycle the lift empty and listen for simultaneous safety cam clicks at three heights, then confirm both release together. Four: inspect equalization cables at every sheave for broken strands, and spin each sheave. Five: look for hydraulic seeps at cylinder rods, fittings, and the power unit.

Six: sight down each column for straightness and inspect baseplate welds for cracks. Seven: check arm pivot pins for slop and look for prior weld repairs. Eight: confirm the overhead shutoff bar or limit switch functions if it is a clearfloor design. Nine: verify the data plate is present and legible, because insurance and any future inspection will ask for it. Ten: ask about the slab it was mounted on and pull one anchor to see what came out. If the seller will not let you do that last one, that tells you something. A used car lift automotive purchase can be a genuinely good deal — we have installed plenty of solid twenty-year-old Rotary equipment that will outlast newer imports. But it has to pass the list. If you want a second opinion before you bid, send us the model, serial, and a few photos of the arms and columns, and we will tell you what we see. We also keep a running guide on annual lift safety inspections if you want the full version.